Integrated logic circuits which may be interfaced with multiple host computer or micro controller systems are prevalent in the current electronics market. To provide flexibility in the use of these circuits, it is often necessary to provide configuration information to the host microcontroller or the circuit itself to designate the configuration of the device in use.
Using a microprocessor-based controller as an example, the approach in the prior art has been to provide pull-up or pull-down resistors which are selectively jumpered to dedicated control or data lines on the microprocessor. This prior art technique is demonstrated in FIG. 1. Typically, a dedicated control line into the microprocessor was required for each configuration parameter. The user selected the configuration by installing a jumper between the control line interconnect and a pull-up resistor or a pull-down resistor on the circuit board. Use of a dedicated control line from the microprocessor for each parameter may have significant impact on the microprocessor connection capacity where numerous configuration parameters are required.
As an example, a microprocessor controlling a generic disk drive controller might require the following configuration information: buffer ram size 8K or 32K bytes; disk drive write format (MFM, RLL or NRZ); designation as drive number 1, drive number 2 or drive number 3; host computer configuration (IBM AT, IBM XT); other. This simple list of configuration parameters would require a minimum of 8 configuration identification lines to designate the selection of the various parameters. In the prior art, this would require 8 dedicated control lines from the microprocessor.
In addition, prior art systems required both a pullup and pull-down resistor to provide determinant identification of each selectable parameter. Providing both a pull-up and pull-down resistor requires additional circuit board space and jumper connection provisions. Further, no default configuration exists and a jumper to either the pull-up or pull-down resistor must be installed.